package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.beans.IntrospectionException;
import java.lang.reflect.*;
import java.sql.SQLException;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws SQLException, IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, InvocationTargetException, ClassNotFoundException {
        //将要去完成对simpleExecutor里的query方法的调用
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }



    @Override
    public <T> T selectOne(String statementId, Object... params) throws SQLException, IllegalAccessException, IntrospectionException, InstantiationException, ClassNotFoundException, InvocationTargetException, NoSuchFieldException {
        List<Object> objects = selectList(statementId, params);
        if(objects.size() == 1){
            return (T) objects.get(0);
        }else{
            throw  new RuntimeException("查询结果为空或者返回结果过多");
        }
    }



    public int update(String statementId, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        int i = simpleExecutor.update(configuration, mappedStatement, params);

        return i;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用JDK动态代理来为Dao接口生成代理对象，并返回


        Object o = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //proxy：当前对象的引用
                //method：当前被调方法的引用
                //args：传递的参数

                //底层还是去执行JDBC代码，也就是query方法。//根据不同情况来调用selectList或者selectOne，然后由他们去调用query
                //准备参数 1：statementid = namespace.id = 接口全限定名.方法名
                //方法名：findAll
                String methodName = method.getName();
                //接口全限定名:com.lagou.dao.IUserDao
                String className = method.getDeclaringClass().getName();
                String statementId = className +"." + methodName;
                //根据statementId获取MappedStatement对象
                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                switch (mappedStatement.getSqlCommandType()) {
                    case INSERT: {
                        // 执行 INSERT 操作
                        return update(statementId, args);
                    }
                    case UPDATE: {
                        // 执行 UPDATE 操作
                        return update(statementId, args);
                    }
                    case DELETE: {
                        // 执行 update 操作
                        return update(statementId, args);
                    }
                    case SELECT:
                        //准备参数 2：params:args
                        //获取被调用方法的返回值类型
                        Type genericReturnType = method.getGenericReturnType();
                        //判断是否进行了 泛型参数化
                        if(genericReturnType instanceof  ParameterizedType){
                            List<Object> objects = selectList(statementId, args);
                            return objects;
                        }else if("java.lang.Integer".equals(genericReturnType.getTypeName())){
                        }
                        return selectOne(statementId, args);
                    default:
                        throw new Exception("Unknown execution method for: " + mappedStatement.getSqlCommandType());
                }
            }
        });
        return (T) o;
    }
}
